The present invention relates to an improved sub-surface, or in-ground/in-water, direct expansion heat pump system incorporating a unique application and combination of sub-surface heat exchange tubing, of compressor sizing, of air handler sizing, of receiver sizing, of oil separator use and oil return location, of additional compressor lubricating oil, of accumulator sizing, of expansion device sizing, of utilizing a particular grout to protect against corrosive elements, of refrigerant operating pressures, and of refrigerant charging, for use in association with direct expansion heating/cooling systems, and in particular for use in association with any deep well direct expansion (“DWDX”) heating/cooling system, or partial geothermal heating/cooling system, utilizing sub-surface heat exchange elements as a primary or supplemental source of heat transfer, together with a means of lowering and extracting the sub-surface components into and out of a well/borehole. A deep well direct expansion system (herein referred to as a “DWDX” system) is herein defined as a direct expansion system which utilizes sub-surface heat exchange tubing in excess of 100 feet deep. The present invention may also be utilized in direct expansion systems 100 feet, or less, in depth (near surface) with improved operational efficiency results.
Ground-source/water-source heat exchange systems typically utilize fluid-filled closed loops of tubing buried in the ground, or submerged in a body of water, so as to either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged tubing. Water-source heating/cooling systems typically circulate, via a water pump, water, or water with anti-freeze, in plastic polyethylene underground geothermal tubing so as to transfer heat to or from the ground, with a second heat exchange step utilizing a refrigerant to transfer heat to or from the water, and with a third heat exchange step utilizing an electric fan to transfer heat to or from the refrigerant to heat or cool interior air space.
Direct expansion ground source heat exchange systems, where the refrigerant transport lines are placed directly in the sub-surface ground and/or water, typically circulate a refrigerant fluid, such as R-22, in sub-surface refrigerant lines, typically comprised of copper tubing, to transfer heat to or from the sub-surface elements, and only require a second heat exchange step to transfer heat to or from the interior air space by means of an electric fan. Consequently, direct expansion systems are generally more efficient than water-source systems because they require less heat exchange steps and because no water pump energy expenditure is required. Additional benefits of a direct expansion type system over a water-source system are: copper tubing is a better heat conductor than most plastic tubing; the refrigerant fluid circulating within the copper tubing of a direct expansion system generally has a greater temperature differential with the surrounding ground than the water circulating within the plastic tubing of a water-source system; generally, less excavation and drilling is required with a direct expansion system and, correspondingly, installation costs are generally lower with a direct expansion system than with a water-source system.
While most in-ground/in-water heat exchange designs are feasible, various improvements have been developed intended to enhance overall system operational efficiencies. Various such design improvements are taught in: U.S. Pat. No. 5,623,986 to Wiggs; in U.S. Pat. No. 5,816,314 to Wiggs, et al.; U.S. Pat. No. 5,946,928 to Wiggs; U.S. Pat. No. 6,615,601 B1 to Wiggs; Wiggs' U.S. patent application Ser. No. 10/073,513; Wiggs' U.S. patent application Ser. No. 10/127,517; Wiggs' U.S. patent application Ser. No. 10/251,190; Wiggs' U.S. patent application Ser. No. 10/335,514; and Wiggs' U.S. patent application Ser. No. 10/616,701; the disclosures of all of which are incorporated herein by reference.
In direct expansion applications, supply and return refrigerant lines may be defined based upon whether they supply warmed refrigerant to the system's compressor and return hot refrigerant to the ground to be cooled, or based upon the designated direction of the hot vapor refrigerant leaving the system's compressor unit, which is the more common designation in the trade.
For purposes of this present invention, the more common definition in the trade will be utilized. Hence, supply and return refrigerant lines are herein defined based upon whether, in the heating mode, warmed refrigerant vapor is being returned to the system's compressor, after acquiring heat from the sub-surface elements, in which event the larger interior diameter, sub-surface, vapor/fluid line is the return line and evaporator, and the smaller interior diameter, sub-surface, liquid/fluid line, operatively connected from the interior air handler to the sub-surface vapor line, is the supply line; or whether, in the cooling mode, hot refrigerant vapor is being supplied to the larger interior diameter, sub-surface, vapor fluid line from the system's compressor, in which event the larger interior diameter, sub-surface, vapor/fluid line is the supply line and condenser, and the smaller interior diameter, sub-surface, liquid/fluid line is the return line, via returning cooled liquid refrigerant to the interior air handler, as is well understood by those skilled in the art. In the heating mode the ground is the evaporator, and in the cooling mode, the ground is the condenser.
Virtually all heat pump systems, including direct expansion heat pump systems, utilize a compressor, an interior heat exchange means, an exterior heat exchange means, thermal expansion devices, an accumulator, a receiver, and refrigerant transport tubing. Generally, most direct expansion systems are designed to utilize, and do utilize, conventionally sized equipment components. For example, a three ton conventional direct expansion system, designed to accommodate a three ton heating/cooling load as per ACCA Manuel J load calculations, or other similar design criteria, typically utilizes a 3 ton compressor, a 3 ton air handler (a common interior heat exchange means), a 3 ton design capacity sub-surface heat exchange means (often about 5 horizontal 100 foot long ¼″ diameter refrigerant grade copper tubes per ton, a 3 ton metering device (typically one self-adjusting thermal expansion valve for each of the cooling and heating segments), a 3 ton accumulator, a 3 ton receiver (with various other receiver designs, claimed or utilized, based upon about a greater or a smaller size of the compressor tonnage size utilized, as explained in U.S. Pat. No. 5,946,928 to Wiggs, which is incorporated herein by reference), and standard 3 ton design refrigerant grade copper transport tubing of varying sizes, all as well understood by those skilled in the art, to and from the compressor unit, the heat exchange means, and the other system components.
Other design improvements for conventional near-surface, direct expansion, heating/cooling systems are also taught in the said U.S. Pat. No. 5,946,928 to Wiggs. Conventional direct expansion systems typically require a relatively large surface area of land within which to bury an array of heat exchange tubing, or require a relatively extensive surface area within which to locate a series of multiple boreholes typically only 50 to 100 feet deep. While for new residential construction on relatively large lots, such designs can be well suited. However, the large surface area excavation requirements are often not well suited for retrofit applications, and are usually not well suited for most commercial applications, due to restricted available land surface areas.
To overcome such conventional direct expansion system application shortcomings, designs have been developed to permit the installation of sub-surface heat exchange tubing in sub-surface tubing installed at depths of 100 feet, or more, such as those designs taught by Wiggs in various of the above-referenced patents and patent applications. However, testing has shown that to successfully operate a deep well direct expansion system with exceptionally high operational efficiencies, a good sub-surface heat exchange system alone is not enough. A unique combination of design load sizing, of heat pump component equipment sizing, of refrigerant tubing sizing, of refrigerant tubing lengths, of refrigerant operating pressures, of refrigerant charging, of additional refrigerant lubricating oil, and of oil separator use must also be employed. Otherwise, the system will be either not operate at all, or will operate at lower than potential optimum efficiencies. In any geothermal heating/cooling system, including a direct expansion system, the best possible operational efficiencies are a high design priority.
Consequently, a design and a means to provide an enhanced operationally efficient direct expansion heating/cooling system, and in particular such a deep well direct expansion (“DWDX”) system with vertically oriented heat exchange tubing, which can eliminate large land surface area requirements, and which can be easily installed in both new construction and retrofit applications would be preferable. Further, a means to protect the sub-surface copper tubing from potentially corrosive elements, and an optional means to access direct expansion sub-surface refrigerant heat exchange tubing for repair work or for replacement purposes, without having to re-excavate or without having to re-drill a deep well, would also be preferable in some situations. The present invention provides a solution to these preferable objectives, as hereinafter more fully described.